The present invention relates to cleaning residual contaminants from semiconductor devices, and more particularly, to a new composition and method for etch removal of undesirable materials from areas near contact openings on wafer surfaces. The invention also relates to the semiconductor structures cleaned in accordance with the formulation and method hereinafter described.
In the formation of contact openings or vias in semiconductor devices used to provide conductor-to-conductor contacts, it is often necessary to etch through one or more layers of insulative material formed over a substrate. FIG. 1 shows a cross section of a portion of a semiconductor device 10 in an intermediate stage of fabrication. The device has a substrate 12. The substrate is formed of a material such as silicon. Field oxide regions 13, transistor gate stacks 15, spacers 17 protecting the gate stacks, and doped regions 19 are formed over the substrate. The substrate 12 also has at least one conductive area in the form of a conductive xe2x80x9cplugxe2x80x9d 21, e.g. a polysilicon plug, formed thereover which has been deposited through afirst layer of insulating material 23, which is usually a type of glass oxide available in the art, for example, Boro-Phospho-Silicate Glass (BPSG), or silicon oxide material such as silicon dioxide or Tetraethylorthosilicate (TEOS). The first layer of insulating material 23 may, in actuality, be formed as one or more layers of insulating material of, for example, BPSG or TEOS. The insulating layer 23 may be anywhere from a few hundred Angstroms to several thousand Angstroms in thickness. The top of layer 23 and the top of plug 21 may also be substantially coplanarized using available methods.
As shown in FIG. 2, a second insulative layer 25 is formed over the first insulative layer 23. The second insulative layer 25 may be comprised of the same or different material than that of the first insulative layer 23, and can also comprise BPSG, for example. A dielectric anti-reflective coating (DARC) layer 27 is formed over the second insulative layer 25 using available methods. The DARC layer 27 is typically comprised of silicon oxynitride and may be a few Angstroms to several hundred Angstroms in thickness. A photoresist layer 29 is patterned over the DARC layer 27 to provide access to the conductive plug 21 as represented by the dotted lines in FIG. 2.
Referring now to FIG. 3, a contact opening 31 is formed through the DARC layer 27 and the second insulative layer 25. The contact opening 31 is preferably formed using available etching methods, in particular dry etching using one or more available fluorinated hydrocarbons that are exposed to acceptable operating parameters. The etch stop is preferably the top of the conductive plug 21. The DARC layer 27 prevents the photoresist layer 29 from being exposed to light which is otherwise reflected off the insulative layer 25, which during the developing of photoresist layer 29 causes it to have an incorrect opening for etching.
As shown in FIG. 4, after formation of the contact opening 31 the photoresist layer may be stripped using available methods. Removal of the photoresist layer leaves the exposed DARC layer 27 over the second insulative layer 25 which must also be removed. The DARC layer 27, comprised of silicon oxynitride, and although a solid dielectric layer it has a tendency to leak at times, and may therefore interfere with subsequent metallization of the contact opening 31, e.g. metallization during capacitor formation. Its removal is therefore highly desirable. At the same, it is also desirable to remove this layer with minimal effect on the second insulating layer 25, e.g. with minimal or no removal of layer 25.
To date, removal of the DARC layer 27 has been achieved using chemical formulations that have included such compounds as ammonia fluoride (NH4F) mixed with phosphoric acid (H3PO4). One reference, U.S. Pat. No. 5,981,401 to Torek et al. describes a method for selective etching of antireflective coatings. However, this document only discloses etch ratios that are greater than 1 or 2. This would indicate that the underlying insulative layer is still being etched at a rather high rate relative to the di-electric anti-reflective coating layer. In addition, the patentees recommend etchant solutions with very high (basic) pH""s to achieve etch rates greater than 1. They disclose pH""s which exceed 11, and desirably are between 11 and 14.
Unfortunately, none of the compositions or methods available in the art have been totally satisfactory in removing the DARC layer, while minimally affecting the underlying insulative layer. Some have been too weakly formulated so that the DARC layer is not adequately removed; others have been too strong or corrosive such that a significant portion of the insulative material is removed as well.
Thus, there exists a need in the art for an improved formulation and method for removing dielectric anti-reflective coating (DARC) layers, as well as other residual debris that may be formed during other stages of semiconductor fabrication, such as during formation of contact openings.
In accordance with the invention, there is set forth a method of removing a dielectric anti-reflective coating comprising contacting the coating with a removal mixture containing tetramethylammonium fluoride and at least one acid selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, citric acid, sulfuric acid, carbonic acid and ethylenediamine tetraacetic acid.
In a further embodiment of the invention a composition suitable for use in removing a silicon oxynitride dielectric anti-reflective coating is provided. The composition comprises about 10 to about 40% of tetramethylammonium fluoride; and about 0.15 to about 6% of at least one acid selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, citric acid, sulfuric acid, carbonic acid and ethylenediamine tetraacetic acid. The composition may also contain from about 1 to about 15% of an oxidizing agent such hydrogen peroxide, ozone, or ammonium persulfate.
The invention also provides a method of removing silicon oxynitride material by contacting it with a mixture of tetramethylammonium fluoride and at least one acid selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, citric acid, sulfuric acid, carbonic acid and ethylenediamine tetraacetic acid. The contacting is performed at a temperature within the range of about 10 degrees C to about 70 degrees C.
Further provided as part of the invention is a method of forming a contact opening in an insulative layer formed over a substrate in a semiconductor device. The method comprises forming a dielectric antireflective coating layer over the insulative layer, and then forming a photoresist layer over the coating layer. The photoresist layer is patterned and exposed to provide an etch mask. A contact opening is then etched through the insulative layer using the etch mask. The photoresist layer is then removed, and the coating layer is contacted with a removal mixture containing tetramethylammonium fluoride and at least one acid selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, citric acid, sulfuric acid, carbonic acid and ethylenediamine tetraacetic acid, with the contacting being sufficient to remove the coating layer.
In addition, the invention provides a method of chemical mechanical planarization. A top portion of a conductive plug is planarized with a top portion of an insulative layer formed over a substrate in a semiconductor device. At least one of the top portions is then contacted with a mixture of tetramethylammonium fluoride and at least one acid selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, citric acid, sulfuric acid, carbonic acid and ethylenediamine tetraacetic acid.
The invention further provides a semiconductor device having a substrate, and a contact opening formed in an insulative layer over the substrate, wherein at least the contact opening or the portion of the insulative layer around the contact opening, and preferably both regions, have been cleaned with a mixture of tetramethylammonium fluoride and at least one acid selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, citric acid, sulfuric acid, carbonic acid and ethylenediamine tetraacetic acid.
Additional advantages and features of the present invention will become more readily apparent from the following detailed description and drawings which illustrate various exemplary embodiments of the invention.